Field of the Invention
The present invention relates to steady state speeds of movement for irrigation systems and more particularly pertains to a new system for achieving and maintaining substantial straight alignment of the spans of an irrigation system with continuous movement over a range of speeds in a forward and reverse movement direction that minimizes or eliminates strenuous and repetitive start-and-stop movements by elements of the irrigation system.
Description of the Prior Art
Mechanized irrigation systems, such as center pivot or lateral move irrigation systems, typically employ a series of pipe spans supported above a ground surface by tower structures that may include wheels or crawler tracks mounted on the tower structures, that are driven to advance the spans about a field in either a forward movement direction or a reverse movement direction. For the purposes of the present invention, the mechanized irrigation system will be referred to as the irrigation system and the pipes and the tower structures supporting the pipes will be referred to collectively as spans. Each of the spans move relatively independently of the other spans, and the movement of the spans is often performed in a follow the leader type manner in which an end span initially advances in either a forward movement direction or reverse movement direction of the irrigation system, and the remaining intermediate spans follow thereafter.
The forward movement direction or reverse movement direction of the irrigation system is dependent on either a clockwise rotation or counter clockwise rotation of the central shafts of the rotors of the span motors connected to reduction gearboxes that drive the rotation of the wheels contacting the ground surface. The direction of the rotation of the central shafts of the rotors of the span motors are conventionally controlled by conductors supplying power, typically, 3-phase, 480 volt AC (alternating current), to the span motors. Conventional 3-phase induction motors provide inherently high starting torques and high efficiency in operation, typically at 60 Hz (cycles per second), on irrigation systems of the prior art and such motors may also be used as the 3-phase span motors of the present invention.
In the case of 3-phase span motors as conventionally used on center pivots, such span motors typically operate at a fixed span motor RPM (revolutions per minute) of approximately 1,750. Gear reduction is provided to achieve a pace of movement over the ground of the wheels of about 0.8 wheel RPM. Such span motors can also easily be reversed (e.g., clockwise rotation of the central shafts of the rotors of the span motors to counterclockwise rotation of the central shafts of the rotors of the span motors). Reversal of the rotation of the central shafts of the rotors of the span motors is accomplished by simply reconfiguring the connections of any two of the three conductors L1, L2, L3 of the 3-phase supply power using a conventional electromechanical contactor device, typically located at a central control panel (not shown). This feature of 3-phase motors facilitates selecting a clockwise rotation or counter clockwise rotation of the central shafts of the rotors of the span motors, and, in turn, selecting either a forward movement direction or reverse movement direction of the irrigation system. A change in either the forward movement direction or reverse movement direction of the irrigation system is controlled conventionally for both the prior art and for the system of the present invention by simply reconfiguring the connections of any two of the three conductors L1, L2, L3 of the 3-phase supply power.
Another convention of irrigation systems for the prior art is the use fixed-speed drive assemblies that may include an alignment detector with one or more single-pole, double-throw (SPDT) switches that are wired to receive either a forward movement direction signal or a reverse movement direction signal depending on either a forward movement direction or a reverse movement direction. These typical SPDT switches control the span motors of the fixed-speed drive assembly on and off while the irrigation system is moving in either a forward movement direction or a reverse movement direction. The discrete forward and reverse movement direction signals are communicated to the switches that each serve to signal two distinct states of alignment to control the 3-phase span motors on and off using a fixed-speed drive controller (e.g., electromechanical contactor or motor starter) of the fixed-speed drive assembly. Such forward and reverse movement direction signals are typically communicated to the switches using separately configured circuits as compared to the three conductors L1, L2, L3 of the 3-phase supply power that are configured to supply electrical power to the span motors.
In an example of the prior art, a forward movement direction signal may be present in a forward movement direction, and a reverse direction signal may be present in a reverse movement direction. In operation, conventional center pivot controls include both a forward movement direction signal and a reverse movement direction signal; however, only one of the two movement direction signals is present in a respective movement direction. Furthermore, the respective forward movement direction signal and reverse movement direction signal are each typically configured to cause the switches to signal the fixed-speed drive controller to control the span motors on and off in an opposite manner with regard to maintaining span alignment. For example, with the same state of alignment, a forward movement direction signal may be configured by the fixed-speed drive controller to control the span motor on and a reverse movement direction signal may be configured by the fixed-speed drive controller to control the span motor off.
The span motor of an intermediate span is typically controlled from span motor on to span motor off and span motor off to span motor on by a fixed-speed drive controller that monitors the output of the corresponding alignment detector that may include a single-pole, double-throw switch. Conventionally, in the prior art, the span motor RPM is not varied other than when the span motor is controlled from span motor on to span motor off and span motor off to span motor on. Such switch signals a discrete (i.e., binary logic, or two-state) on/off signal switch state to cycle control the span motor in an on/off manner. The switch may be located at spans adjacent to the flexible junctures where adjacent spans are interconnected. Relative movement of adjacent spans actuates these switches and, for example, enables the signaling of two distinct states of alignment of adjacent interconnected spans, such as that caused by the forward movement of an outer span about the flexible juncture of two adjacent spans. For example, the wheels of a lagging intermediate tower structure are driven in a forward movement direction by the rotation of one or more cams, rotated by one or more rods (e.g., mechanical linkage), that rotate against the roller-actuating arm of a corresponding switch that causes the internal contacts of the respective switch to close in a conventional single-pole, double-throw method that results in an “on” signal switch state controlling the 3-phase span motor on. Furthermore, in this example, the supply power supplied to the span motor is configured to rotate the central shaft of the rotor of such span motor in a clockwise rotation and, thereby, the span is driven in a forward movement direction by a respective fixed-speed drive assembly until a substantial straight alignment is restored between the adjacent spans (i.e., respective intermediate tower structure not lagging and not leading). The switches signal two distinct states of alignment based on either a forward movement direction or a reverse movement direction and on a closed switch contact or an opened switch contact that results in either a span motor “on” control or a span motor “off” control.
The fixed-speed drive assemblies incorporating the span motors are, therefore, alternately and repeatedly controlled on and controlled off by way of a discrete “on” signal switch state or “off” signal switch state. The wheels of the intermediate tower structures may each be driven in either a forward movement direction or a reverse movement direction at a uniform speed with closed switch contacts and stopped with opened switch contacts. This process is repeated by each successive intermediate tower structure of the irrigation system until all of the spans are brought into substantial straight alignment. Each time an intermediate tower structure is advanced in either a forward movement direction or a reverse movement direction, a new distinct state of alignment is signaled by the corresponding switch and the process is repeated.
In center pivot irrigation systems, the radially-outermost tower structure or end tower structure typically leads the movement of the spans of the irrigation system, while in a lateral move irrigation system either one of the end tower structures typically leads the movement of the spans of the irrigation system. In a center pivot irrigation system, the outermost or end span wheel track has the largest circumference; and, therefore, the end span has the farthest distance to travel. In the systems of the prior art the intermediate spans, having relatively smaller wheel track circumferences, can always keep up with the speed of the end span while using substantially the same fixed-speed span motors, assuming similar wheel tire sizes and gearing ratios.
This conventional manner of movement and substantial straight alignment of the spans of irrigation systems requires countless starts-and-stops by the intermediate tower structures, and the corresponding fixed-speed drive assemblies that move them. The number of repeated on-and-off control cycles of the corresponding span motor providing the movement for a respective intermediate tower structure can exceed one thousand a day during continuous operation. This repeated on-and-off control cycling of the corresponding span motors, which is repeated every day, all day, that the irrigation system is operating, causes excessive wear on the electrical components, structural components, and mechanical parts of the fixed-speed drive assembly, especially the span motors, knuckles and gearboxes transferring power to the wheels.
To mitigate the stress on the irrigation system caused by the repetitive start-and-stop movement of fixed-speed drive assemblies typically utilizing alignment detectors as discussed above, movement control systems have been proposed to provide a relatively smooth and continuous movement of the intermediate spans and their respective intermediate tower structures. These continuous movement control systems typically employ potentiometers or other analog sensors, such as capacitive displacement sensors, strain gauge sensors, non-contact proximity sensors or other devices capable of quantifiably measuring a precise degree of span alignment. Analog alignment sensor signals vary in magnitude in direct correlation or proportion to the degrees of deviation in alignment of one span with respect to adjacent interconnected spans. Such analog alignment sensor signals are monitored and processed by variable-speed drive controllers configured to vary aspects of the supply power (i.e., vary the speed) furnished to the corresponding span motor. This, in turn, varies the span motor RPM that, in turn, varies the RPM of the wheels in response to changing analog alignment sensor signals. These analog type sensors are in lieu of typical rod and switch actuators and cams or similar discrete signaling devices that merely use a switch to signal if the state of alignment is beyond a preset maximum value, as is the case with the conventional systems of the prior art for center pivot irrigation system movement control systems.
The variations in the magnitude or intensity of analog sensor signals are monitored and processed by variable-speed drive controllers that, in turn, vary aspects of the supply power (i.e., vary the speed) furnished to the corresponding span motors turning the wheels of the intermediate tower structures in substantially direct correlation or proportion to the degrees of deviation in alignment as detected and outputted by the analog sensors, such that detection of greater angles of deviation in alignment of the interconnected spans results in relatively faster span motor speeds, and detection of relatively lower angles of deviation in alignment results in relatively slower span motor speeds. Such means of varying span motor speeds in direct proportion to the degrees of deviation in alignment as detected and outputted by the analog sensors (i.e., the selected speed of the variable-speed drive controller is based upon the alignment) to maintain substantial straight alignment of the spans with continuous movement requires the span motors to constantly transition between faster speeds and slower speeds (i.e., transient state speeds of movement) as opposed to evolving to unchanging fixed-speeds (i.e., steady state speeds of movement).
Krieger (U.S. Pat. No. 6,755,362), Malsam (U.S. Patent App. Pub. No. 2013/0018553) and Grabow (U.S. Patent App. Pub. No. 2013/0253752) have proposed to provide a relatively smooth and continuous movement and substantial straight alignment of spans using potentiometers or other analog sensors or, in the case of Grabow, GPS (global positioning system) data is used as a means of generating analog alignment sensor signals for varying span motor speeds in direct proportion to the degrees of deviation in alignment.